1. Field of the Invention
The present invention relates to a frame structure of an uplink control information transmission channel in a communication system called a multi-input/multi-output (MIMO) system in which transmitting and receiving ends commonly use multiple antennas.
2. Description of the Related Art
FIGS. 1 and 2 show a related art MIMO communication system employing a PARC (Per-Antenna Rate Control) method.
The PARC refers to a method based on the construction of a V-BLAST (Vertical Bell Laboratories Layered Space Time) system, one of conventional techniques of the MIMO system, in which symbols of signals are differently channel-coded and modulated according to each transmission antenna in a transmitting end with reference to channel information determined at a receiving end and then the corresponding signals are transmitted through each transmission antenna.
FIG. 1 is a view showing the construction of the transmitting end of the related art MIMO communication system employing the PARC method. The operation of the MIMO communication system employing the PARC method will now be described with reference to FIG. 1.
High speed data streams sequentially generated from the transmitting end is demultiplexed through a demultiplexer DEMUX 110 so as to be transmitted from each of multiple transmission antennas. Herein, the demultiplexing means dividing consistent data into a plurality of sub-data according to a determined regulation. FIG. 1 shows two antennas for the sake of explanation.
The demultiplexed sub-streams of each transmission antenna are coded and interleaved in signal processors 121 and 122, and then mapped to a symbol, respectively.
The mapped symbols are inputted to a spreader 131 in which a spreading codel is multiplied thereto, coded into a scrambling code, and then transmitted to respective transmission antennas 161 and 162.
If a user occupies 10 channels discriminated by the spreading code, the divided sub-streams are divided again into 10 sub-streams, respectively. Respective divided data symbols are inputted into spreaders 131˜133, in which each spreading code 1˜10 is multiplied thereto, added in adders 141 and 142, coded into a scrambling code, and then, transmitted through respective transmission antennas 161 and 162. Herein, generally, one scrambling code is allocated per user. The number of bits allocated to the transmission antennas 161 and 162 can differ depending on a designated data rate.
The coding is made only in a temporal dimension, so its data restoration performance is not as high as that in the space-time coding which is used in a single-rate system. The coding in the temporal domain allows post-decoding interference cancellation, by which performance of a receiver is enhanced.
FIG. 2 is a view showing the construction of a related art receiving end of the MIMO communication system employing the PARC method. The operation of the receiving end of the MIMO communication system employing the PARC method will now be described with reference to FIG. 2.
After the data is demultiplexed and then coded into the scrambling code in the transmitting end, the signals of each transmission antenna can be independently decoded in the receiving end as shown in FIG. 2.
In other words, when the reception antennas 211 and 212 receive the symbol, symbols of each channel are estimated in a symbol detector according to a minimum mean square error (MMSE) method, despread and multiplexed by despreaders 241 and 242 and a multiplexer 250 so that a signal with respect to one antenna can be detected, and the detected signal is relocated (demapped), deinterleaved and then decoded in a signal processor 260.
Thereafter, a signal with respect to the antenna is reconfigured in a signal remover 270 based on the decoded bits and then the reconfigured signal is removed from a reception signal stored in a buffer.
Signals of other antennas are processed in the same manner and along the same path, and then coupled by a coupler 280.
The PARC is a MIMO system technique for a high speed downlink packet access (HSDPA) proposed by Lucent, which allows, unlike the V-BLAST, each transmission antenna to use a different data transmission rate to thereby increase a transmission capacity. In this case, the transmitting end transmits an encoded signal independent by transmission antennas.
The PARC system is different from the V-BLAST system, the existing single-rate MIMO technique in the aspect that each antenna has a different data transmission rate (modulation and coding).
Namely, the PARC system allows each antenna to control the data transmission rate independently more minutely, which leads to enhancement of a substantial transmission capacity of an overall system. In this case, although more bits are required for informing about a state of channels of each antenna than in techniques proposed for the single rate MIMO system, a reference set can be determined.
In other words, in the PARC system, in order to determine a MCS (modulation & Coding Scheme) set valid for each antenna, an SINR (Signal to Interference Noise Ratio) of each transmission antenna as received by each reception antenna is calculated.
At this time, in order to select a channel coding and modulation method to be used at each antenna, the SINR received through each antenna is measured, based on which a combination of a channel coding method and a modulation method to be used at each antenna is selected.
[Table 1] and [Table 2] show examples of combinations of transmission rate of transmitted data and an MCS in the MIMO system having four transmission antennas and four reception antennas.
TABLE 1Data rateCodingbps/Hz(Mbps)Constellationrate37.216 QAM¾24.816 QAM½1.53.6QPSK¾12.4QPSK½0.51.2QPSK¼
TABLE 2Rate:IndexMbpsAnt1Ant2Ant3Ant4128.83333226.43323326.43233426.42333524.02332624.02323724.02233821.62232921.622231019.222221122.821.5331220.421.5231318.021.5221419.221.51.521516.821221625.21.53331722.81.53231822.81.52331920.41.52232018.01.52222119.21.521.522221.61.51.5332321.61.51.5332416.81.51.5222514.41.51.5212615.61.51.51.522715.61.51222824.013332921.613233021.612333119.212233216.812223315.61221.53415.6121.523518.011.5233615.611.5223720.40.52333815.60.52223914.4334014.4334112.0324212.0324312.0234412.023459.622469.622478.421.5488.421.54910.81.535010.81.53518.41.52528.41.52539.613549.613557.23567.23574.82584.82593.61.5603.61.5612.41622.41631.20.5641.20.5
As shown in [Table 1], when the modulation method is performed at 16QAM and a coding rate is 3/4, the data rate is the maximum, which corresponds the number of transmission bits per unit frequency of 3. And this case can be matched to a case where the SINR calculated at the reception antenna is the maximum.
The next fastest data rate is when the modulation method is performed at the 16QAM and the coding rate is 1/2, which corresponds the number of transmission bits per unit frequency of 2. In this manner, each number of transmission bits per unit frequency is determined according to the modulation methods and the coding rates, and the number of transmission bits per unit frequency is allocated to the four transmission antennas of [Table 2].
[Table 2] shows examples of combinations of transmission rates in the system using four transmission antennas and four reception antennas. In [Table 2], the index ‘1’ indicates that the number of transmission bits per unit frequency of each of the four transmission antennas is 3 and a data transmission rate is the highest, namely, 28.8.
In such a 4×4 PARC system (namely, the PARC system having four transmission antennas and four reception antennas), in case of the indices from 1 to 38 having a good channel situation because of the relatively shorter distance between the transmitting end and the receiving end, the four transmission antennas can be all used to transmit data, but in case of the indices from 39 to 54 having a bad channel situation because of a relatively longer distance between the transmitting end and the receiving end, two antennas with the larger number of transmission bits per unit frequency are selected from the four transmission antennas to transmit data therethrough.
In the afore-mentioned related art, a serial-to-parallel stage for distributing data generated in a transmitting end to each transmission antenna is provided so that signals can be independently transmitted from each transmission antenna, and a receiving end detects the signals transmitted from each transmission antenna and processes them. In addition, each transmission antenna of the transmitting end can use a different coding and modulation method, which is determined by the receiving end and feeds corresponding information back to the transmitting end.
FIG. 3 illustrates a structure of an uplink channel in the related art MIMO system.
With reference to FIG. 3, a dedicated physical channel (DPCH), among uplink channels transmitted from a receiving end (namely, a terminal) to a transmitting end (namely, a base station) includes 15 slots (305), and each slot (305) includes a dedicated physical data channel (DPDCH) 310 and a dedicated physical control channel (DPCCH) 320.
The DPCCH includes a pilot symbol 322 for estimating channel information, frame merge information (transport format combination indicator (TFCI) 324 having SF (spreading factor) information of an uplink channel, feedback information (FEB) 326, namely, a feedback signal including and carrying information for transmit diversity, and power control bits (TPC: Transmit Power Control) 328 having power control information.
The DPDCH 310 includes substantial data 312 of a user.
FIG. 4 illustrates a structure of the uplink channel in a related art HSDPA system.
With reference to FIG. 4, in the conventional HSDPA system, in order to allow each transmission antenna of the transmitting end to use a different coding and modulation method, certain information is fed back from the receiving end to the transmitting end through an HS-DPCCH (HS-Dedicated Physical Control Channel) 400.
At this time, the HS-DPCCH 400 includes a frame structure having two frames: a field 410 to which ACK/NACK for an HARQ (Hybrid Automatic Retransmission Request) is allocated and a field 420 to which CQI (Channel Quality Information) is allocated. The ACK/NACK has the size of one slot and the CQI has the size of 2 slots.
The related art HSDPA uses a single transmission antenna, so it can transmit the feedback information through one HS-DPCCH.
However, in case of a multiple input/output systems, namely, the MIMO system, because a modulation method, a coding rate and the ACK/NACK information can be set to be different with respect to multiple transmission antennas, a control signal with respect to each transmission antenna needs to be fed back.